Ski boots fitted with means for cooperation with the top of the ski, and indeed for being secured onto the latter when the bindings are closed over the soles of said boots, are well known. The boot described in French Patent N.degree. 2 407 681 may be mentioned as an example of precisely this type; in this kind of construction, it is basically the position maintenance of the foot which is sought, simultaneously with the closing of the rear binding over the heel of the boot. For this purpose, a movable part is provided which protrudes beneath the sole in the rest position and retracts into said sole under the locking tension exerted by the binding. This movable part is arranged so as to act in coordination with the binding support plate, i.e., in the heel area, and actuates a foot-positioning device.
In the case of the boot disclosed in U.S. Pat. No. N.degree. 3,893,683 it is the unlocking of the boot from the ski when the skier executes pronounced forward bends which is sought. For this purpose, the shaft of the boot has a lower extension piece which come into contact with the top of the ski in the rest position and which projects outward as soon as said shaft pivots forward. Since the shaft forms a lever, it is necessary only that it pivot to a certain degree in order to cause the heel of the boot to be raised off the ski, and thus, the release of said boot by opening the binding.